1. Field of the Invention
The present invention relates to centrifugal pumps, and more particularly, to an improved impeller for use in a centrifugal pump. The present invention finds particular application in conjunction with an aircraft fuel pump, and it will be described with particular reference thereto. However, it is to be appreciated that the present invention is also amenable to other like applications.
2. Discussion of the Art
The structure and operation of centrifugal pumps is well known in the art. Briefly, fluid generally enters a pump inlet in an axial direction and due to the rotation of the impeller the fluid centrifugally flows radially outward through a set of channels defined between impeller blades. The fluid discharges from the impeller around the peripheral edge of the impeller. The centrifugal action of the fluid flowing outwardly through the channels creates a suction at the central area of the impeller which serves to continuously draw more fluid into the inlet of the pump.
The fluid discharged from the impeller is at a significantly higher pressure than the fluid entering the pump inlet. The major portion of the energy imparted to the fluid is converted to a pressure head by means of a volute, diffuse, or other system.
Impellers may generally be classified according to their flow arrangements. Single-suction impellers receive fluid through a single inlet on one face of the impeller. Double-suction impellers generally have fluid flowing onto opposed faces of the impeller. The fluid streams flowing into each face of a double-suction impeller are usually commingled within impeller fluid channels or at the periphery of the impeller before exiting the pump.
Centrifugal pumps may additionally be classified as either single-stage pumps or multi-stage pumps. Single-stage pumps are generally defined as those in which the pressure head was developed by a single pass through only a single impeller. Multi-stage pumps generally refer to pumps using two or more impellers operating in series. Additionally, a single impeller, double suction pump has been, heretofore, generally classified as a single-stage pump.
Multi-stage pumps are often used in applications that require large volumes of liquid to be delivered at high pressures. Each stage incrementally imparts rotational energy into the fluid thereby increasing the amount of pressure of the fluid at each stage. Although the delivery of a high volume of fluid at high pressures is desirable, several disadvantages are present in the prior art.
One disadvantage of multi-stage pumps is that substantial internal energy losses result from using additional impellers because each impeller frictionally interfaces with the surrounding pump casing or housing. The mechanical drag results in lower pump efficiency.
Another disadvantage is that each additional impeller stage adds volume and weight to the overall pump assembly. Increased volume or size may prevent installation of the pump unit in tight-fitting applications. Increased weight may cause inefficiencies in particular applications such as for use as an aircraft fuel pump where the load capacity of the aircraft is limited.
Therefore, it is desirable to provide an improved impeller for use in a centrifugal multi-stage pump that overcomes these problems and others.
In accordance with the present invention, an improved impeller for use in a single-impeller, multi-stage centrifugal pump is provided for minimizing these and other disadvantages of the prior art.
More particularly, a preferred embodiment of the present invention has an impeller provided with multiple inlets and corresponding sets of discharge ports. Multiple pump stages are accomplished by successively passing the fluid through the impeller by entry into the various inlets of the impeller.
A preferred embodiment of the centrifugal pump includes a housing having a pump inlet and a pump outlet that communicate with an internal chamber. A rotatable shaft drives a generally cylindrical impeller operatively received in the internal chamber. The impeller includes a first impeller face, a second impeller face opposite from the first impeller face, and a radial peripheral edge extending around the circumference of the impeller and interconnecting the first and second impeller faces. The impeller also includes a first impeller inlet located on one of the first and second impeller faces and a second impeller inlet located on one of the first and second impeller faces. Additionally, a first and second set of impeller outlet ports are located on the impeller. The first set of channels communicate between the first impeller inlet and the first set of impeller outlet ports disposed in the impeller while the second set of channels communicate between the second impeller inlet and the second set of impeller outlet ports disposed in the impeller.
According to a preferred method of the present invention increased pressure of a fluid in a centrifugal pump having a single impeller is provided. The method includes the steps of providing fluid through a pump inlet to a first impeller inlet. Fluid exiting the impeller through a first set of discharge ports is directed to a second inlet for a second pass through the same impeller. The fluid then exits the impeller through a second set of discharge ports at an increased pressure. Finally, the fluid is directed to a pump outlet. Of course, additional passes through the same impeller are possible.
A primary advantage of the present invention is reduced overall efficiency losses due to mechanical drag from using the subject single-impeller, multi-stage pump of the present invention.
A further advantage is realized by the multi-pass single impeller obtaining high discharge pressures without requiring a large impeller diameter.
Another advantage of the present invention over the prior art is that the overall pump weight is reduced.
Still another advantage is that the overall size of the pump is reduced.
Still other features and benefits of the invention will be apparent to those skilled in the art upon reading and understanding the following detailed description.